The effect of changing interfacial tension on the shape of the red cell

Previous biophysical research on the equilibrium of the red cell membrane in the normal biconcave, and the other shapes assumed in osmotic swelling, has led to a relation for the dimple region, between the tension in the membrane, its curvature, and an internal pressure. The relation is tested on a new shape produced by adding 0.004% by volume of Tween 80. The opposite membranes near the axis of revolution of the cell become parallel over a disc of diameter 2.6 μ, at a distance of 0.77 μ apart (30% less than the nearest distance in normal cells). The 'dimple' region becomes more like a 'moon crater'. The volume of the cell is not significantly altered, but the surface area increases by about 14%. The shape is consistent with a decrease in interfacial tension of the membrane, and the area increase is similar to that found by Seeman for agents which enter into the membrane. The hypothesis of internal structure across the central part of the cell, indicated by previous studies of birefringence, is supported by the observations on this new shape.